JP2017076027A - Liquid crystal display device, television receiver and liquid crystal backlight control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen the dynamic range of brightness by enabling stable lighting control while curtailing variation in chromaticity in brightness adjustment of a liquid crystal backlight.SOLUTION: Regarding the backlight that adjusts brightness by causing light emitters aligned for each of a plurality of areas which are formed by dividing a display screen in the horizontal and vertical directions to emit light, the brightness is calculated for each of the plurality of areas of the backlight on the basis of an image signal. When the brightness calculated on the basis of the image signal is equal to a first threshold or more, a lighting time of the light emitters is controlled according to the calculated brightness by fixing a driving current during one frame period, while when the brightness is less than the first threshold, the driving current of the light emitters is controlled according to the calculated brightness by fixing the lighting time during the one frame period.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a liquid crystal display device, a television receiver, and a liquid crystal backlight control method.

  In recent years, in a liquid crystal display device used for a television receiver, high dynamic range technology characterized by high brightness and high contrast has attracted attention. In particular, backlight control technology is important for high dynamic range display. At present, in the backlight control method, an LED (Light Emitting Diode) is often used, and there is a method of dividing the screen vertically and horizontally and adjusting the brightness for each area. As a method for adjusting the brightness of the LED, there are a method for controlling the lighting time of the LED during one frame period, a method for controlling the LED driving current, and the like in accordance with the average luminance of the video data in the corresponding area.

Japanese Patent Laid-Open No. 2002-324685 JP2013-062192A

  By the way, in the brightness adjustment of the liquid crystal backlight by the LED, the method of controlling the lighting time of the LED within one frame period has a problem that it becomes difficult to perform dimming with stable luminance as the lighting time becomes shorter. Further, the method for controlling the LED drive current has a problem that the change in chromaticity increases when the change in current value is large.

  The purpose of this embodiment is to enable stable light control while suppressing changes in chromaticity in adjusting the brightness of a liquid crystal backlight using LEDs, and thereby a liquid crystal display device and a television that can widen the dynamic range of brightness An object of the present invention is to provide a John receiver and a liquid crystal backlight control method.

  A liquid crystal display device according to an embodiment includes a liquid crystal display panel in which a plurality of liquid crystal cells are arranged vertically and horizontally in a display screen, and a plurality of areas arranged in a horizontal and vertical direction in the display screen. And a backlight that adjusts the brightness by emitting light emitting elements arranged in each area and inputs a video signal and supplies a drive signal corresponding to each pixel of the video signal to each cell of the liquid crystal display panel Then, a liquid crystal driving unit that controls the transmission amount of each cell, and calculates the luminance for each of the plurality of areas of the backlight based on the video signal, and drives the light emitting element to obtain a brightness corresponding to the luminance And a backlight driving unit. When the luminance calculated based on the input video signal is greater than or equal to a first threshold for each of a plurality of areas, the backlight driving unit applies a driving current during one frame period to the light emitting element. The lighting time is controlled according to the calculated luminance, and when the luminance is less than the first threshold, the lighting time during one frame period is fixed to the light emitting element. Then, the drive current is controlled according to the calculated luminance.

The block diagram which shows the structure of the television receiver by which the liquid crystal display device which concerns on embodiment is mounted. 1 is a block diagram showing a configuration of a liquid crystal display device according to a first embodiment. The flowchart for demonstrating specifically the drive current determination process of the drive current and lighting time determination part shown in FIG. The flowchart for demonstrating concretely the lighting time determination process of the drive current and lighting time determination part shown in FIG. The figure which shows the brightness control method by the backlight drive part of 1st Embodiment. The figure for demonstrating the outline | summary of the drive current control and lighting time control by the backlight drive part of 1st Embodiment. 9 is a flowchart for specifically explaining drive current determination processing in the liquid crystal display device according to the second embodiment. 9 is a flowchart for specifically explaining lighting time determination processing in the liquid crystal display device according to the second embodiment. The figure for demonstrating the outline | summary of the drive current control and lighting time control by the backlight drive part of 2nd Embodiment. The block diagram which shows the structure of the liquid crystal display device which concerns on 3rd Embodiment. The flowchart for demonstrating specifically the drive current determination process of the drive current and lighting time determination part shown in FIG. The flowchart for demonstrating concretely the lighting time determination process of the drive current and lighting time determination part shown in FIG.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration of a television receiver on which the liquid crystal display device according to the embodiment is mounted. In FIG. 1, a TV tuner 11 receives a digital broadcast wave reception signal from an antenna (not shown) and selects a broadcast signal of a designated channel. The selected broadcast signal is sent to the demodulation / decoding unit 12. The demodulation / decoding unit 12 performs demodulation processing and error correction decoding processing on the input broadcast signal to convert it into a TS (Transport Stream) signal. This TS signal is sent to the video / audio separator 13. The video / audio separation unit 13 separates the input TS signal into an audio stream and an audio stream. The separated video signal is converted from the video stream into video data of a predetermined resolution by the video decoder 14 and sent to the liquid crystal display device 15 to be displayed as a video on the liquid crystal display panel. The separated audio signal is converted from an audio stream into audio data in a designated mode by an audio decoder 16 and sent to an audio output device 17 for sound reproduction by a speaker.

  Hereinafter, liquid crystal display devices according to first to third embodiments applied to the television receiver having the above-described configuration will be described.

(First embodiment)
FIG. 2 is a block diagram showing a specific configuration of the liquid crystal display device 15 according to the first embodiment. In FIG. 2, reference numeral 151 denotes a liquid crystal display panel having a liquid crystal layer sandwiched between a pair of substrates, and a predetermined number of liquid crystal cells arranged vertically and horizontally in a display screen, and 152 is arranged on the back surface of the liquid crystal display panel 151 for display. This is a backlight substrate in which the inside of a screen is divided into a plurality of areas in the horizontal and vertical directions, and LEDs are arranged for each area to enable adjustment of luminance.

  The input video data is sent to the liquid crystal driving unit 153 and the backlight driving unit 154. The liquid crystal driving unit 153 supplies a driving signal corresponding to each pixel of video data to each cell of the liquid crystal display panel 151 to control the transmission amount of each cell. The backlight driving unit 154 calculates the luminance of the corresponding area from the video data for the LEDs arranged in each area of the backlight substrate 152, and drives the LEDs so that the brightness corresponding to the luminance is obtained.

  In the backlight driving unit 154, the luminance calculating unit 1541 calculates the luminance of the backlight in each area based on the video of the input video data. The drive current / lighting time determination unit 1542 determines the LED drive current and lighting time during one frame period of each area based on the luminance calculated for each area. The drive current control unit 1543 controls the drive current for the LEDs in each area based on the value determined by the determination unit 1542. The lighting time control unit 1544 sends the driving current supplied to the LEDs in each area to the ON / OFF switching unit 1545 arranged at the subsequent stage of the driving current control unit 1543 at the lighting time in one frame period determined by the determination unit 1542. Based on this, an ON / OFF switching signal is sent. In this way, the LED drive current and lighting time of each area are controlled to have the calculated luminance.

  FIG. 3 is a flowchart for specifically explaining the drive current determination process of the drive current / lighting time determination unit 1542 of FIG. In FIG. 3, when the luminance calculation result L of each area is obtained by the luminance calculation unit 1541 (step S11), the luminance calculation result L is compared with a threshold value Th for determining whether or not the luminance calculation result L enters low luminance (step S12). ). In each area, when the luminance calculation result L is equal to or greater than the threshold Th (Yes), the LED drive current is fixed to a maximum value or the like to obtain a fixed current value (step S13). If it is smaller than the threshold Th (No), the drive current value is increased or decreased according to the previously determined luminance-current characteristic (luminance-current conversion) (step S14). There is a method of performing this luminance-current conversion using an LUT (Look up Table) or the like.

  FIG. 4 is a flowchart for specifically explaining the lighting time determination process of the drive current / lighting time determination unit 1542 of FIG. In FIG. 4, when the luminance calculation result L of each area is obtained by the luminance calculation unit 1541 (step S21), the luminance calculation result L is compared with a threshold value Th for determining whether or not the luminance calculation result L enters low luminance (step S22). ). In each area, when the brightness calculation result L is equal to or greater than the threshold Th (Yes), the lighting time of the LED in one frame period is increased or decreased according to the previously determined brightness-lighting time characteristics (brightness-lighting time conversion) (step S23). If it is smaller than the threshold value Th (No), it is fixed to the minimum value or the like and set as a fixed lighting time (step S24).

  That is, in the present embodiment, as shown in FIG. 5, a hybrid control method is employed that has both a method for controlling brightness with a drive current and a method for controlling brightness with a lighting time. In FIG. 5, if it is assumed that the drive current and the brightness of the LED and the lighting time and the brightness of the LED are in a proportional relationship, an area surrounded by a square in the figure represents the brightness during one frame period. Then, as shown in FIG. 6, in the middle / high luminance region (luminance is greater than or equal to the threshold Th), the lighting time control (driving current is fixed) is selected, and in the low luminance region (luminance is less than the threshold Th), the drive current control ( The lighting time is fixed). In the method of controlling the brightness of the liquid crystal backlight by the LED, the method of controlling the lighting time of the LED within one frame period has a problem that it becomes difficult to perform dimming with a stable luminance as the lighting time becomes short. Since the area has a fixed minimum lighting time capable of stable light emission and the lighting time control is limited to the middle / high luminance area, the luminance can be stably adjusted. Further, in the method of controlling the LED driving current, there is a problem that the chromaticity varies according to the change of the current, but in the middle to high luminance region where the chromaticity variation is easily perceived, the current value is fixed, Since the current control is limited to the low luminance region, the subjective influence of the chromaticity variation can be reduced. As a result, the chromaticity variation can be suppressed by performing the lighting time control from the middle to the high luminance, and the luminance dynamic range can be widened by reducing the luminance in the dark portion.

  Therefore, according to the liquid crystal display device according to the present embodiment, in the brightness adjustment of the liquid crystal backlight by the LED, it is possible to perform stable dimming to low luminance while suppressing change in chromaticity from intermediate to high luminance, As a result, the luminance dynamic range can be widened.

(Second Embodiment)
In the second embodiment, the threshold value to be compared with the luminance is set in two stages, and the brightness is adjusted more gently. Since the specific configuration of the liquid crystal display device 15 according to the present embodiment is the same as that of the first embodiment shown in FIG. 2, the description thereof is omitted here.

  FIG. 7 is a flowchart for specifically explaining the drive current determination process of the drive current / lighting time determination unit 1542 in the second embodiment. In FIG. 7, when the luminance calculation result L of each area is obtained by the luminance calculation unit 1541 (step S31), the luminance calculation result L is compared with a second threshold Th2 that is larger than the first threshold Th1 (step S32). In each area, when the luminance calculation result L is equal to or greater than the second threshold Th2 (Yes), the drive current value is increased or decreased according to the first luminance-current characteristic obtained in advance (first luminance-current conversion) ( Step S33). If it is smaller than the second threshold Th2 (No), it is compared with the first threshold Th1 (step S34). In each area, when the luminance calculation result L is equal to or greater than the first threshold Th1 (Yes), the LED drive current is fixed to the maximum value or the like to obtain a fixed current value (step S35). If it is smaller than the first threshold Th1 (No), the drive current value is increased or decreased according to the second luminance-current characteristic obtained in advance (second luminance-current conversion) (step S36).

  FIG. 8 is a flowchart for specifically explaining the lighting time determination process of the drive current / lighting time determination unit 1542 in the second embodiment. In FIG. 8, when the luminance calculation result L of each area is obtained by the luminance calculation unit 1541 (step S41), the luminance calculation result L is compared with a second threshold Th2 that is larger than the first threshold Th1 (step S42). In each area, when the luminance calculation result L is equal to or greater than the second threshold Th2 (Yes), the first fixed lighting time is set to the maximum value or the like (step S43). If it is smaller than the second threshold Th2 (No), it is compared with the first threshold Th1 (step S44). In each area, when the luminance calculation result L is equal to or more than the first threshold Th1 (Yes), the lighting time of the LED in one frame period is increased or decreased according to the previously determined luminance-lighting time characteristic (brightness-lighting time conversion). (Step S45). If it is smaller than the first threshold value Th1 (No), it is fixed to the minimum value or the like as the second fixed lighting time (step S46).

  That is, in the present embodiment, as shown in FIG. 9, in a high luminance region (luminance is equal to or greater than the second threshold Th2), driving current control is selected as a fixed maximum lighting time, and chromaticity variations are easily perceived. In the middle luminance region (the luminance is less than the second threshold and the first threshold or more), the driving current is fixed and the lighting time control is selected, and the light is stable in the low luminance region (the luminance is less than the first threshold Th). The drive current control is selected as a fixed minimum lighting time capable of light emission. In this case, since the drive current control is adopted in the high luminance region and the low luminance region, the subjective influence of the chromaticity variation in each region can be reduced. In addition, since the lighting time is controlled in the intermediate luminance region, the luminance can be stably adjusted.

  Therefore, according to the liquid crystal display device according to the present embodiment, in the brightness adjustment of the liquid crystal backlight by the LED, it is possible to perform stable dimming while suppressing a change in chromaticity from low luminance to high luminance. The luminance dynamic range can be widened.

(Third embodiment)
In the third embodiment, in addition to the processing of the first embodiment shown in FIG. 2, the backlight lighting luminance of the entire screen is added, and the power consumption of the backlight is obtained based on the luminance, and the power consumption is defined. The driving current control and the lighting time control are appropriately switched in a state where the power source capacity is less than.

  FIG. 10 is a block diagram showing a specific configuration of the liquid crystal display device 15 according to the third embodiment. In FIG. 10, the same parts as those in FIG. 2 are denoted by the same reference numerals, and redundant description is omitted here.

  In the backlight drive unit 154 shown in FIG. 10, the power consumption calculation unit 1546 inputs the luminance value for each area calculated by the luminance calculation unit 1541, adds the lighting luminance in the entire screen, and based on the addition result Calculate the power consumption of the backlight. The drive current / lighting time determination unit 1542 is based on the backlight power consumption obtained by the full screen addition unit 1546 together with the brightness calculated for each area, and the LED drive current and lighting time during one frame period of each area. To decide. Specifically, when the calculated brightness is equal to or greater than the threshold and the power consumption is within a specified power supply capacity, the driving current is fixed and the lighting time is controlled by the first luminance-lighting time characteristic. To do. When the calculated luminance is less than the threshold value, the lighting time is fixed to the second time, and the driving current is controlled by the second luminance-driving current characteristic.

  FIG. 11 is a flowchart for specifically explaining the drive current determination process of the drive current / lighting time determination unit 1542. In FIG. 11, when the luminance calculation result L of each area is obtained by the luminance calculation unit 1541 (step S51), the luminance calculation result L is compared with a threshold value Th1 for determining whether or not the luminance calculation result L enters low luminance (step S52). ).

  In each area, when the luminance calculation result L is equal to or greater than the threshold Th1 (Yes), the power consumption based on the luminance of the entire screen calculated by the power consumption calculation unit 1546 is compared with the specified power supply capacity (step S53). Here, it is determined whether L is less than the threshold Th2 higher than the threshold Th1 (Step S54). If less than Th2 (No), the LED drive current is fixed (Step S55), and the power consumption is less than the power supply capacity. If L is equal to or greater than the threshold value Th2 (Yes), the drive current value is increased or decreased according to the first luminance-current characteristic obtained in advance for the LED drive current (step S56).

  In step S52, if it is smaller than the threshold Th1 (No), the drive current value is increased or decreased according to the second luminance-current characteristic obtained in advance (step S57).

  FIG. 12 is a flowchart for specifically explaining the lighting time determination processing of the drive current / lighting time determination unit 1542. In FIG. 12, when the luminance calculation result L for each area is obtained by the luminance calculation unit 1541 (step S61), the luminance calculation result L is compared with a threshold value Th for determining whether or not the luminance calculation result L enters low luminance (step S62). ).

  In each area, when the brightness calculation result L is equal to or greater than the threshold Th1 (Yes), the power consumption based on the brightness of the entire screen calculated by the power consumption calculation unit 1546 is compared with the power supply capacity of the LED drive power supply (step S63). ). Here, it is determined whether or not L is less than the threshold Th2 higher than the threshold Th1 (Step S63), and if L is lower than Th2 (Yes), the lighting time is increased or decreased according to the luminance-lighting time characteristics obtained in advance (Step S63). S64). If L is equal to or greater than the threshold Th2 (Yes), the lighting time of one frame period is fixed to the first time (step S66).

  Moreover, in step S62, when smaller than threshold value Th1 (No), lighting time is fixed to 2nd time (step S67).

  In FIGS. 11 and 12, the driving current is increased when L is greater than Th2 and less than the power supply capacity. However, the lighting time corresponding to L = Th2 is set to be smaller than the maximum in advance, and the power is supplied when L is greater than Th2. There is no problem as the lighting time is further increased when the capacity is lower than the lower capacity.

  Therefore, according to the liquid crystal display device according to the above-described embodiment, the processing is performed in the same manner as in the first embodiment, thereby suppressing the change in chromaticity from the middle to the high luminance and expanding the dynamic range of the luminance. The backlight can be dimmed with a high brightness. Furthermore, when high luminance display is performed with power consumption less than the power supply capacity, display with higher luminance can be achieved by increasing the drive current. Accordingly, it is possible to perform backlight dimming with a stable luminance from a low luminance to a high luminance while enabling a further high luminance display within a range that the power supply capacity satisfies.

  In each embodiment, how to allocate the current and lighting time after calculating the luminance of the backlight in each area is not limited to this.

  As mentioned above, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 11 ... TV tuner, 12 ... Demodulation / decoding part, 13 ... Video | audio / audio separation part, 14 ... Video decoder, 15 ... Liquid crystal display device, 151 ... Liquid crystal display panel, 152 ... Backlight board, 153 ... Liquid crystal drive part, 154 ... Backlight drive unit, 1541 ... Luminance calculation unit, 1542 ... Drive current / lighting time determination unit, 1543 ... Drive current control unit, 1544 ... Lighting time control unit, 1545 ... ON / OFF switching unit, 1546 ... Power consumption calculation unit , 16 ... audio decoder, 17 ... audio output device.

Claims (9)

A liquid crystal display panel in which a plurality of liquid crystal cells are arranged vertically and horizontally in a display screen;
A backlight that is arranged on the back surface of the liquid crystal display panel, divides the display screen into a plurality of areas in the horizontal and vertical directions, and emits light emitting elements arranged in each area to adjust the brightness; and
A liquid crystal driving unit that inputs a video signal and supplies a driving signal corresponding to each pixel of the video signal to each cell of the liquid crystal display panel to control a transmission amount of each cell;
Calculating a luminance for each of a plurality of areas of the backlight based on the video signal, and comprising a backlight driving unit that drives the light emitting element to have a brightness corresponding to the luminance;
The backlight driving unit fixes a driving current during one frame period to the light emitting element when the luminance calculated based on the video signal is equal to or higher than a first threshold for each of a plurality of areas. Then, the lighting time is controlled according to the calculated luminance, and when the luminance is less than the first threshold, the lighting time in one frame period is fixed to the light emitting element. A liquid crystal display device that controls the drive current according to the calculated luminance.   The backlight driving unit further controls the light emitting element when the luminance calculated based on the video signal is equal to or higher than a second threshold higher than the first threshold for each of a plurality of areas. The liquid crystal display device according to claim 1, wherein the lighting time during one frame period is fixed and the drive current is controlled according to the calculated luminance.   The backlight driving unit further calculates the power consumption of all areas from the brightness calculated for each of the plurality of areas, and the video for each of the plurality of areas in a state where the power consumption is less than a prescribed power supply capacity. When the luminance calculated based on the signal is equal to or higher than the second threshold value higher than the first threshold value, the lighting time in one frame period is fixed and the drive current is controlled according to the calculated luminance value. The liquid crystal display device according to claim 1. A liquid crystal display panel in which a plurality of liquid crystal cells are arranged vertically and horizontally in a display screen, and arranged on the back of the liquid crystal display panel, the display screen is divided into a plurality of areas in the horizontal and vertical directions, and arranged for each area. A backlight for adjusting the luminance by emitting light from the light emitting element, and a video signal of a television broadcast reception program are input, and a driving signal corresponding to each pixel of the video signal is supplied to each cell of the liquid crystal display panel. A liquid crystal driving unit for controlling a transmission amount of the backlight, and a backlight driving for calculating the luminance for each of the plurality of areas of the backlight based on the video signal and driving the light emitting element so as to obtain a brightness corresponding to the luminance. A television receiver using a liquid crystal display device comprising:
The backlight driving unit fixes a driving current during one frame period to the light emitting element when the luminance calculated based on the video signal is equal to or higher than a first threshold for each of a plurality of areas. Then, the lighting time is controlled according to the calculated luminance, and when the luminance is less than the first threshold, the lighting time in one frame period is fixed to the light emitting element. A television receiver that controls the drive current according to the calculated luminance.   The backlight driving unit further controls the light emitting element when the luminance calculated based on the video signal is equal to or higher than a second threshold higher than the first threshold for each of a plurality of areas. The television receiver according to claim 4, wherein the lighting time during one frame period is fixed and the driving current is controlled according to the calculated luminance.   The backlight driving unit further calculates the power consumption of all areas from the brightness calculated for each of the plurality of areas, and the video for each of the plurality of areas in a state where the power consumption is less than a prescribed power supply capacity. When the luminance calculated based on the signal is equal to or higher than the second threshold value higher than the first threshold value, the lighting time in one frame period is fixed and the drive current is controlled according to the calculated luminance value. The television receiver according to claim 4. A liquid crystal display panel in which a plurality of liquid crystal cells are arranged vertically and horizontally in a display screen, and arranged on the back of the liquid crystal display panel, the display screen is divided into a plurality of areas in the horizontal and vertical directions, and arranged for each area. A backlight for adjusting the luminance by emitting light from the light emitting element, and inputting a video signal to supply a driving signal corresponding to each pixel of the video signal to each cell of the liquid crystal display panel to transmit a transmission amount of each cell Used in liquid crystal display devices to control
For each of a plurality of areas, the luminance is calculated for each of the plurality of areas of the backlight based on the video signal, and when the luminance calculated based on the video signal is equal to or greater than a first threshold, the light emitting element On the other hand, when the driving current during one frame period is fixed and the lighting time during one frame period is controlled according to the calculated luminance, and the luminance is less than the first threshold, the light emission A liquid crystal backlight control method for controlling the drive current according to the calculated luminance while fixing the lighting time during one frame period for an element.   Further, for each of a plurality of areas, when the luminance calculated based on the video signal is equal to or higher than a second threshold value that is higher than the first threshold value, the light emitting element is in one frame period. The liquid crystal backlight control method according to claim 7, wherein the driving current is controlled according to the calculated luminance while the lighting time is fixed.   Further, the power consumption of all areas is calculated from the brightness calculated for each of the plurality of areas, and the power consumption is calculated based on the video signal for each of the plurality of areas in a state where the power consumption is less than a prescribed power supply capacity. The liquid crystal back according to claim 7, wherein when the luminance is equal to or higher than a second threshold value higher than the first threshold value, the lighting time in one frame period is fixed and the driving current is controlled according to the calculated luminance. Light control method.

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